1. Field of the Invention
The present invention relates to a vehicle air-conditioning system of a dual air-conditioner type provided with cooling evaporators at both a front seat air-conditioning unit and rear seat air-conditioning unit wherein, at the time of heating, gas refrigerant delivered from the compressor (hot gas) is directly introduced to the front seat evaporator so as to provide a hot gas heater function.
2. Description of the Related Art
In the past, there has been known a vehicle air-conditioning system of the dual air-conditioner type which directly introduces a gas refrigerant delivered from a compressor (hot gas) to an evaporator at the time of heating so as to provide a hot gas heater function (see Japanese Unexamined Patent Publication (Kokai) No. 2001-130245).
In the related art, a hot gas bypass passage for directly connecting a compressor delivery side to an inlet side of a front seat evaporator bypassing the refrigerant radiator, that is, the condenser, has been provided, a heating use pressure reducing device has been provided at the hot gas bypass passage, and a cooling use solenoid valve and heating use solenoid valve have been provided for opening and closing the refrigerant passage and hot gas bypass passage to the evaporator.
In the front seat air-conditioning unit, a hot water type front seat heating use heater core is arranged at the downstream side of the front seat evaporator. Therefore, when heating at the winter, when the temperature of the hot water circulating in the heating use heater core is lower than a predetermined temperature (at the time of starting warmup of the engine), the cooling use solenoid valve is closed and the heating use solenoid valve is opened, whereby the high temperature delivery gas refrigerant (hot gas) of the compressor is made to flow into the hot gas bypass passage.
Further, by reducing the pressure of this hot gas by a heating use pressure reducing device, then directly introducing this to the front seat evaporator, the heat is radiated from the gas refrigerant to the air-conditioning air at the front seat evaporator so as to exhibit the hot gas heater function.
Further, the rear seat air-conditioning unit similarly has arranged in it a rear seat evaporator and a hot water type rear seat heating use heater core, but the hot gas bypass passage is connected to only the inlet side of the front seat evaporator and therefore the hot gas heater function is exhibited at only the front seat evaporator. This is because of the following reason.
That is, among the vehicle air-conditioning front side and rear side air-conditioning units, the front seat air-conditioning unit can be switched between introduction of inside air and outside air. At the time of heating in the winter, usually the outside air introduction mode is selected to stop fogging of the window. Therefore, by introducing low temperature outside air, the heating thermal load of the front seat air-conditioning unit is greatly increased compared with an inside air type rear seat air-conditioning unit.
Therefore, by concentrating the hot gas heater function at only the evaporator of the front seat air-conditioning unit, it is possible to effectively improve the heating performance of the front seat air-conditioning unit with its large heating thermal load by the hot gas heater function. This is due to the above.
Further, in the above related system, in the refrigeration cycle, the downstream side of the condenser has a receiver arranged in it. The inlet sides of the front seat evaporator and the rear seat evaporator have pressure reducing devices comprised of thermal type expansion valves arranged at them. Further, the outlet pipes of the front seat evaporator and rear seat evaporator are connected to a low pressure gas-liquid separator (accumulator). The outlet part of this low pressure gas-liquid separator is connected to the intake side of the compressor. Further, the outlet pipe of the rear seat evaporator has arranged at it a check valve for preventing backflow of the refrigerant from the low pressure gas-liquid separator to the rear seat evaporator side.
At the time of heating by the hot gas heater cycle, however, the refrigerant delivered from the compressor is passed through the hot gas bypass passage and directly introduced to the inlet side of the front seat evaporator, so the refrigerant delivered from the compressor flows bypassing the condenser etc. Therefore, there was the problem that the refrigerant accumulated in the condenser (dormant) could not be ejected to the hot gas heater cycle side and the amount of circulating refrigerant of the hot gas heater cycle became insufficient.
Therefore, at the time of start of heating by the hot gas heater cycle, it may be considered to set the refrigeration cycle forcibly at the cooling mode for exactly a predetermined time to pass the refrigerant delivered from the compressor through the condenser side to circulate it and recover the condenser side dormant refrigerant at the front seat evaporator side.
However, in a vehicle air-conditioning system of the dual air-conditioner type provided with cooling evaporators at both a front seat air-conditioning unit and a rear seat air-conditioning unit, if setting the system to the cooling mode at the time of startup of heating at cold times to recover the dormant refrigerant in this way, since the cooling thermal load is small, the high/low differential pressure of the cycle becomes extremely small and the amount of circulating refrigerant is small. In addition to this, the rear seat evaporator is arranged at a position far away from the compressor compared with the front seat evaporator, so the pressure loss of the refrigerant passage of the rear seat evaporator is large. As a result, even if setting the system to the cooling mode to recover the dormant refrigerant at the time of startup of heating, it is difficult to recover the refrigerant dormant at the rear seat evaporator. Conversely, along with setting the cooling mode, sometimes the refrigerant flowing into the rear seat evaporator ends up becoming newly dormant at the rear seat evaporator.